How to query a custom post type with a taxonomy filter but display post type archive page?

Question

I'm filtering the main query of Jigoshop with my own taxonomy with this hook (The file responsible for Jigoshop queries that I'm hooking, Jigoshop hooks onto WP 'request' filter):

add_filter( 'loop_shop_tax_query', 'my_loop_shop_tax_query', 11 );
function loop_shop_tax_query( $request )
{
    $region = 'dublin';
    if ( ! empty( $region ) ) {
        $request[] = array(
            'taxonomy'  => 'product_region',
            'field'     => 'slug',
            'terms'     => $region,
            'operator'  => 'IN',
        );
    }

    return $request;
}

I want to filter every Jigoshop query this way (all products display, category display & search display). This is working as intended but wp_title() in the html head is causing the error:

Notice: Undefined property: stdClass::$labels in /var/www/wp/wp-includes/general-template.php on line 658

Notice: Trying to get property of non-object in /var/www/wp/wp-includes/general-template.php on line 658

I've tracked this down in general-template.php and is_post_type_archive() is returning true even though get_tax() is also returning true. get_queried_object() is returning my taxonomy object (normally the Jigoshop product custom post type object).

I need get_queried_object() to still return the Jigoshop product custom post type object and get_tax() should return false, I want to filter the posts with my taxonomy but I want to keep displaying a post type archive (is this even possible?)

Just before the request is sent back to WP for 'request' filter, it looks like this:

Array ( [post_type] => product [post_status] => publish [posts_per_page] => 12 [orderby] => post_date [order] => asc [tax_query] => Array ( [relation] => AND [0] => Array ( [taxonomy] => product_region [field] => slug [terms] => dublin [operator] => IN ) ) [meta_query] => Array ( [0] => Array ( [key] => visibility [value] => Array ( [0] => visible [1] => catalog ) [compare] => IN ) ) [post__in] => Array ( [0] => 293 [1] => 291 [2] => 289 [3] => 18 [4] => 0 ) )

I hope this isn't too specific and makes sense, I'm really at my wit's end here, any help would be greatly appreciated.